Helper drive



Aug. '14, 1945. w. R. HARRIS HELPER DRIVE Filed July 28, 1943 2 Sheets-Sheet 1 HMJ? Q 5,45 5H4 WITNESSES: INVENTOR 5?..5/ h/a/rerE Harv-A5,

BY W M M a. 7'

ATTORNEY g- 14, 1945. w. R. HARRIS 2,382,415

HELPER DRIVE Filed July 28, 1943 2 Sheets-Sheet 2 fig 2.

M07 \lllll EF'Z F/ EXH Q fies 19. 3 E I765 e6 WITNESSES: INVENTOR zffi h 0///'/. Harr/S.

[ m BY W F.4d a.

ATTORNEY Patented Aug. 14, 1945 HELPER DRIVE Walter R. Harris, Wilkinsburg, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application July 28, 1943, Serial No. 496,405

21 Claims.

My invention relates to electric motor control systems for machine plants or units in which a machine part is to be driven in a, given fixed or adjustable speed relation to another driven machine part. In its more specific aspects, the invention relates to systems of the just-mentioned type in which one of a group of correlated machine parts is driven by a main or master drive furnishing the predominant amount of driving energy, while another machine part is provided with an auxiliary or helper drive which performs a more or less auxiliary driving effort. Such helper drives, controlled in dependence upon the operation of. a master drive, are used, for instance, in machine units of the type in which a web or strand element, or a material to be formed into a strand element, is passed over rotating rolls, or through sets of rolls while in contact or working engagement with the peripheral roll surfaces. Rollingmills, coatin machines, waxing machines, printing presses ,and papermaking machines are examples of this type of machine; and the invention, in one of its more particular aspects, concernsitself with machine units of the latter type with particular reference to paper-making machines.

in paper machines, the wet pulp or paper stock is usually entrained by a traveling foraminous strand, such as a band of felt or a wire mesh (Fourdrinier Wire) so as to form a wet coatin on the strand element. The strand is driven by means of a roll, and a number of other rolls or the like cylindric machine parts are provided for guiding the strand through one or several presses for removing water from the stock or otherwise working on. the stock to convert it into a selfsupporting web of paper. This web, still in the wet state, is then passed through roll presses, driers and calendars to assume the desired final consistency and strength. Most of these machine sections contain rolls, some of which are actuated by a drive while others revolve merely by virtue of their frictional engagement with the travelin strand or web or by frictional engagement through the web with another roll. As a rule, the driven rolls operated from a line shaft which in turn is driven by a steam engine, electric motor or other available source of motive power.

It has been known to apply electric helper drives to one or several rolls for various auxiliary or corrective purposes. For instance, to roll presses, having the lower roll power driven from the line shaft, a helper drive has been applied for actuating the top roll in a given speed relation to the power or master drive of the lower roll in order to eliminate slippage and irregularities or stresses in the strand or sheet material which are apt to occur if friction is exclusively relied upon for driving the top roll.

These helper drives, as heretofore in use, in clude a generator coupled with the line shaft of the paper machine to generate a current of variable voltage dependent upon the speed of the line shaft. An electric motor whose speed is responsive to voltage'is fed from the generator and coupled with the roll to be controlled by the helper drive. As a result, the energization of the motor and hence its speed are dependent upon the speed of the master drive or line shaft, a separate booster generator and suitable control equipmentbeing provided to make up for the IR drop in the helper drive system.

This known type of helper drive is required to operate over a considerable speed range, and it is necessarythat the booster voltage and the generator voltage be correctly proportioned to assure that the operating adjustment is maintained over this speed range. Since the booster voltage should be proportional to the operating load, the

drive is likely to get out of adjustment if the loads are changed, since the machine operators often know little or nothing about the proper control of electrical equipment. Also, in some cases where the line-shafting and mechanical parts do not have enough power to drive the power suppling DC generator, a separate motor generator set has been used which necessitated the use of a pilot generator to obtain the correct voltage for all operating speeds. This complicates the equipment and makes adjustments more difficult. I

It is an object of my invention to provide an electric drive and control system for a machine which is to be driven in a given relation to a separately or independently driven other machine, and to permit varying the speed over a considerable range while maintaining the desired correlation of the two drives at all operating speeds, and largely independent of load variations.

An object, allied to the foregoing, is to permit adjusting and varying the datum value of the torque or driving effort of the helper or auxiliary drives without foregoing the just-mentioned independence from speed or load variations.

Another object of the invention is to provide an automatic control system for accurately maintaining a constant torque or driving effort of a helper drive motor independent of speed or load variations of a correlated master drive.

A further object oi the invention is concerned with machine units having one of several cooperative machine parts driven by a master drive for supplying a major amount of driving energy while another of these machine parts is driven by a helper drive supplying auxiliary or corrective driving energy: this object aims at the provision of a control system for maintaining the helper drive at a constanttorque or at a chosen speed relation to the master drive independently of such load variations as are incident to normal operation, and also securing this relation after the occurrence of load changes of considerable magnitude and suddenness.

It is also an object, in union with any of the foregoing aims, to provide a system of the type here referred to with a control for automatically changing from the adjusted normal torque or correlation of the two drives to another relation more appropriate for starting or slowing-down conditions, thereby improving the stability of operation by preventing undue stress. during the periods of such transient conditions.

A further object of my invention is to provide a master drive and helper drive system with a variable-voltage control for accurately maintaining a selective speed relation between master and helper drive while affording a gradual and stepless voltage control over a wide range of speeds and voltages under avoidance of regulating contactors in the electric control circuits proper.

Referring to paper-making machines, one of the more specific objects of the invention lies in the provision of voltage-responsive, variablespeed motors as a helper drive for rolls coacting with master-driven rolls or with the strand or web elements transported essentially by such master-driven rolls, the essence of this object being to secure a fine regulation of the helper drive motor so as to maintain a selected speed ratio and/or constant torque regardless of the speed of the controlling master drive and with an accuracy and stability far superior to the known helper drive systems aforementioned.

These and other objects of my invention, as well as its essential features and elements for achieving these objects, will become apparent from the followin description of the embodiments illustrated in the drawings, in which:

Figure l is a diagrammatic representation of the wet end sections of a paper-making machine having a master drive and a helper drive interlinked by a control system exemplifying the invention;

Fig. 2 is a separate circuit diagram of the same control system showing the essential electric elements more in detail and in an elemental straight-line representation; while Fig. 3 is a straight-line circuit diagram showing another embodiment of a helper drive system according to the invention, this system being also applied to the paper-making machine of Fig. l but serving to operate a series of operating rolls different from the one driven by the system of Fig. 2.

Referring at first to Fig. l, I have illustrated the wet end sections and some adjoining sections of a paper-making machine. The fluid pulp is supplied to a series of vats, denoted by VAT, each having a cylinder mould CMi, CMZ and CMS,

stock when revolving. An endless belt FT! of felt or other foraminous material is kept in engagement with the cylinder moulds CMI, CM! and CMS by means of guide rolls GRI, GR! and (3R3, respectively. The felt F'Il passes over a suction drive roll SDR, between a set of baby presses BPI, BP! and BPS, further between the rolls MPI and MP2 of a first main press, thence returning to the cylinder moulds over a series of guide rolls GI, G2, G3 and G4. A second endless belt of felt or the like material, denoted by FM, passes through the baby presses and the first main press together with the felt FT! and is guided by guide rolls G5 and G8.

The lower roll MP! of the first main press is driven by a master drive and the suction drive roll SDR by a helper drive, as will be more fully described hereinafter. Due to this drive, and in cooperation with several helder drives to be described in a later place, the felt FTI travels in the direction of the arrow Al when in operation, and the felt FT2, entrained by friction, moves in the direction of arrow A2.

During this operation, an amount of stock is transferred by the moulds CMI, CM! and 0M3 from the vats VAT to the surface of the felt F'Il, the total amount of stock thus applied to the felt depending upon the number and operating speed of the moulds. When passing over the suction drum SDR, part of the excess water is removed from the stock. While passing further between the felts FTI and FT! and the baby presses BPI, BP2 and BP3, the stock is freed of more water. When leaving the first main press MPH-MP2, the stock is sufllciently condensed to form a web, denoted by WEB, which, though still wet and oi. low strength, is sufficiently solidified and selfsupporting to travel to the subsequent sections of the machine without assistance by felt supports. The web is passed between the rolls SH and SP2 of a second main press and thence through additional pressing, dryin and calendering sections, one of these sections being represented in the illustrated embodiment by a dual press composed of three cooperating press rolls DPI, DP! and DP3. The web, upon leaving the dual press, continues its travel in the direction of the arrow A3.

The drive of the main press roll MP! will now be described in detail. The driving energy for the first main press, as well as for a number of other sections of the machine unit, is derived from a line shaft LSH which is driven by a line shaft drive LSD of adjustable speed, here represented diagrammatically by a motor. The line 4 shaft drive may consist of any suitable source of respectively, partly immersed in the stock. Each mould consists of a revolvable roll whose surface is covered by a wire mesh to entrain part of the motive power, such as a steam engine, internal combustion engine, turbine or electric motor. Speed change gears or the like may be provided between the drive and the line shaft, if necessary, for obtainin the desired speed variations.

The line shaft LSH is connected to the machine parts to be driven by means of belt drives. One of such drives is arranged between the line shaft and the bottom roll MPI of the first main press. A pulley Mi is mounted on the line shaft LSH and connected by an endless driving belt MB wltha driven pulley M2 which is coupled with the press roll MP! over a coupling MCL and an intermediate transmission represented by a bevel gear MGR and a connecting shaft MS, the latter being indicated by a dot-and-dash line. An electric limit switch LSW is associated with the coupling MCL so that the switch contacts are open when the coupling is in disconnected position, and closed when the coupling' is closed. Switch LSW lies in an electric circuit C3, whose purpose will be referred to in a later place.

The line shaft LSH is similarly provided with additional belt drives for actuating other sections of the paper machine. One of these additional drives comprises a line shaft pulley SI, an endless belt SB, a driven pulley S2, a coupling SCL, a bevel gear SGR and a transmission S3 for actuating the bottom roll SPI of the second main press. A third belt drive from a line shaft pulley DI over a belt DB, a driven pulley D2, 9. coupling DCL, a bevel gear DGR and a shaft D3 serves to drive the roll DP3 of the dual press. Further belt drives may be provided for connecting the line shaft with other sections (not illustrated) of the machine unit.

As already mentioned, the machine unit illustrated in Fig. 1 contains several helper drives in. addition to the main or master drive effected by the line shaft. One of these helper drives serves to supply auxiliary driving power to the suction drum SDR to maintain the drum at a given speed relation to the operation of the first main press,

in order to eliminate at any occurring operating speed a slippage or creeping apt to strain the traveling felt or the paper stock deposited thereon. This helper drive includes an electric direct current motor HDM connected to the suction drum shaft SDS by a coupling HCL. Before describing the other element of the helper drive coacting with the motor HDM, some other helper drive motors shown in Fi 1 may be mentioned.

A set of helper drive motors HMI, l-IM2 and HM3 is provided for controlling the rotation of the cylinder moulds CMI, CM2 and CM3 respectively. Each of these motors is connected with the appertaining cylinder by a transmission indicated schematically by dot-and-dash line connections SHi, SHZ and 8H3, respectively. The motors HMl, HM2 and HM3 are controlled by an electric system which is illustrated in Fig. 3 and will be explained below in conjunction with that figure.

Another helper drive motor HM! and a corresponding transmission 8H4 serve to supply auxiliary driving power to the top roll MP2 of the first main press, while similar motors HMS and HMS with transmissions SE5 and 81-16 are applied for driving the top r011 SP2 of the second main press and the roll DPI of the dual press, respectively. The control systems for motors HMS, HMS and HMS are similar to those. described hereinafter, and hence not separately illustrated in the drawings.

The helper drive and control system of the suction drum SDR, as shown in Fig. 1, contains a main direct current generator GEN for feeding the helper drive motor HDM with current of variable voltage. The feed circuit connecting the generator GEN with the motor HDM is denoted by Cl; it includes a measuring resistor R6 in series connection. The armature of the main generator GEN is driven, through pulleys Li and L2 and a belt LB, from the line shaft LSH so that the generator speed is proportional to the speed of the line shaft and, hence, to that of the main press roll MP! driven thereby. As a result, the generated voltage supplied to the output or feed circuit Cl is dependent upon the speed of the master drive effective on roll MPl. However, the just-mentioned feed voltage of circuit Cl is also dependent upon the excitation of the generator field. This excitation is supplied by a regulating circuit C2 and produced by a regulating DC generator REG. The regulating generator REG forms part of a motor-generator set, and is coupled with a motor MOT which is fed from a current source ACS, preferably an alternating current line, and operates at constant speed. The set includes also an exciter generator EXC which represents a DC source of constant voltage and serves to feed a branched circuit C3. Circuit C3 contains the limit switch LSW and a control relay COR aside from other circuit elements still to be discussed. The above-mentioned electric apparatus and circuits are interlinked electrically and electromagnetically in a manner more clearly apparent from Fig. 2.

The diagram of Fig. 2 represents the same electric drive and control system as is shown in Fig. 1 for controlling the helper drive motor HDM of the suction drum SDR in dependence upon the master drive effected by the line shaft LSH on the roll MPI, of the first main press. These machine elements are also indicated and marked by the same reference characters in Fig. 2. Other parts of the system are also denoted by corresponding reference characters when representing the same elements in these two figures.

According to Fig. 2, the helper drive motor HDM has its armature HDA acted upon by two field windings MFI and MFZ, the former being series-connected in the feed circuit Cl while the latter is a shunt-type winding and separately energized from the exciter circuit C3 over a regulating rheostat MRH. The armature GNA of the main generator GEN, driven from the line shaft LSH by the aforedescribed means, here denoted schematically by a .dot-and-dash line L3, is energized by a generator field winding GEF which is connected in the regulator output circuit C2 in series with a resistor R2.

The regulating generator REG has its armature RGA connected with the regulator circuit C2 and represents its current source. This regulator REG has three field windings RFI, RF2 and RF3. RFI is a self-energizing field winding and seriesconnected in the regulator circuit C2. The resistance of circuit CI, including the field windings GEF and RFi, is adjusted by means of resistor R2 so that the resistance line lies on the saturation curve. Thus the regulator tends to maintain its output current at a given value because of the self-energizing field. The other two regulator windings, (pilot field winding) RF2 and RF3 (pattern field winding), are in the nature of shunt windings and wound for counteracting each other as to their inductive effect on the regulator armature RGA. That is, at a proper relative excitation of the shunt windings RF2 and are, their effects are balanced and, hence, inactive as regards the control of the output voltage of the regulator.

Field winding RFL is connected across the resister Rl. Since the voltage drop across this resistor is a measure of the current in the feed circuit C9, the excitation of the regulator field winding RF? is also proportional to this current.

' The winding RF3 is connected to the exciter circult C3 by circuit means described below, so as to be energized by an adjustable standard or pattern voltage which, as a rule, remains constant during the normal operation of the control system.

The exciter EXC for supplyin the circuit C3 with current of constant voltage has its armature EXA connected in series with a field winding EFI. A shunt field winding EFZ is connected in parallel to the exciter circuit C3 with a regulating rheostat ERH arranged in the shunt circuit. The exciter armature EXA and the regulator armature RGA are mounted on the shaft RSH of the motor MOT connected to the line ACS. Due to the constant speed of this drive, the output voltage of the exciter EXC remains constant. The magnitude of this voltage can be adjusted by varying the adjustment of the exciter rheostat ERH.

Connected across the circuit C3 is a series arrangement of a resistor R3, a potentiometer POT and another resistor R4. This arrangement is tapped between POT and R4 and at a slide contact of the potentiometer. The two taps are connected with the regulator Winding RF! (pattern field winding) over the contacts RCI and RC2 of the control relay COR. Contact RCI is closed and contact RC2 open when the relay is inoperative. Both contacts are connected with a relay armature RAR which is controlled by a relay coil RCL. The coil RCL is connected to the exciter circuit C3 over the line switch LSW. When the exciter EXC is in operation but the line switch LSW open, the coil RCL is not energized, so that the relay contacts RCI and RC2 assume the illustrated position. In this position, the potentiometer tap at POT is ineffective, while the tap point between POT and R4 is connected through contacts RCI with the pattern field winding RF3. Consequently, the pattern field is now excited by the relatively low voltage drop across resistor R4. This resistor is calibrated for standstill conditions of the paper machine. That is, this calibration and the corresponding control effect produced by the pattern field take care of preventing undue stretching or creeping of the felt FII (Fig. 1) apt to occur during standstill conditions,

When closing the coupling MCL (Fig. 1) of the master drive, the limit switch LSW is also closed and the relay coil RCL (Fig. 2) energized. The coil attracts.the relay armature RAR and opens contact RCI while closing the contact RC2. In the relay position now reached, the tap between POT and R4 is disconnected from the pattern field winding RF3 and the latter switched over to the adjustable contact of the potentiometer POT. As a result, the pattern voltage now effective across the field winding RF3 is determined by the voltage drop between the potentiometer contact and the remote end of resistor R4. This voltage drop is larger than the voltage previously applied to R'FS, and can be varied by adjusting the potentiometer contact of POT down to a minimum determined by the magnitude of the resistor R3.

Reviewing now the operating of the helper drive and control system as a whole, let us assume that the line shaft drive LSD of the paper machine is in normal operation and the line shaft LSH rotating at normal speed with the coupling MCL open and, hence, the press rolls MP1 and MP2 at rest (Fig. 1). Let us further assume that the motor MOT of the motor-generator set is switched in and has reached full speed so as'to keep the regulator REG and exciter EXC in operative condition. The armature GNA of the main generator GEN (Fig. 2) is also assumed to Cir thereby causing the felt F1! to begin its travel, the limit switch LBW is also closed. The relay coil RCL (Fig. 2) is now energized, contact RCI opened and contact RC2 closed. This adjusts the pattern voltage in field winding RF: to the higher value selected at POT and places the control system in normal operating condition. The regulator REG supplies a controlled voltage to the main generator GEN which in turn feeds the helper drive motor HDM with current of variable voltage. The speed of the helper drive motor depends on the coaction of two controlling effects, one being constant for determining an adjustable basic or datum component, the other being vari-. able and controlled by the output voltage of the main generator GEN. The constant control effeet on the motor speed is produced by the energization of the motor shunt field MFI adjusted at MRI-I. The voltage supplied to the motor by the main generator GEN, in turn, is also determined by two diiferent control effects. One of these efiects is furnished by the driving connection L3 of the generator GEN with the line shaft LSH and tends to produce a voltage component in proportion to the speed of the master drive.

' The other controlling determinant of the feed voltage in circuit Cl is the energization of the generator field GEF. This energization, supplied by circuit C2 from the regulator, is again dependent on two control biases, aside from the stabilizing action of the self-energizing field winding RFI. These regulating biases are those produced by the differentially-wound and hence counteracting pilot and pattern field windings RFZ and RF3 which, as explained before, respond to the magnitude of the feed current measured by RI and to the selected adjustment of the potentiometer POT, respectively.

Let us assume that the contact of potentiometer POT is set for energizing the pattern field winding RF3 so that a given current intensity, say twenty amps, in the feed circuit Cl is necessary to energize the pilot winding RF! up to the same field strength. I! the generator voltage of GEN is too low to pass a current of this magnitude through circuit Ci, the pattern field of RF2 will be stronger than the pilot field of RF3 and thus will cause the regulator armature RGA to build up in voltage. As a result, the generator voltage of GEN will also increase until the right current is obtained in the feed circuit Cl. Then the differential fields RM and RF3 of the regulator are balanced and ineffective as regards the regulator output voltage in C2. Consequently, the regulatory function of REG is now ended, and nothing further will happen as long as the datum current of twenty amps. is maintained. The self-energizing field RFI tends to stabilize this current 'in circuit C2.

Conversely, if the feed current in Cl is too high, the pilot field of RF2 will be stronger than the pattern field of RF3 and the voltage of the main generator GEN will be forced down by regulator action until the two fields RF! and RF3 again balance each other.

By virtue of this regulating action, th helper drive system maintains the torque or driving ef-- fort of the helper drive motor at a constant value independent of speed variations or load variations of the master drive over the entire range of operating speeds of the paper machine. That is, considerable speed variations are permissible with a system of this type without appreciable inaccuracy of control. All control functions are performed by stepless operation and without the use of control contacts or relays in the regulating network proper. No booster or pilot generators are required, and all essential operating adjustments can be made by means of rheostats or the like adjustable impedance members.

While the foregoing description has been specific as to the details of the embodiment exemplified by Fig. 2, it will be understood that a sysgenerator may form part of a separate motorgenerator set or be driven by the constant-speed motor of the regulating generator. Furthermore,

the self-exciting field winding of the regulating generator may be designed as a shunt field instead of providing the above-described series excitation. According to another possibility, the system may serve for the control of a plurality of helper drive motors acting on different parts of the machine unit. Further modifications applicable in a system of the type here explained relate to the adjustment of the pilot and pattern fields of the regulator. Since the action of these two fields is differential, it is obvious that the adjustment by a rheostat or potentiometer need not necessarily be effected in the circuit of the pattern field Winding of the regulator, but may also be assigned to the circuit of the pilot field or to both field circuits. Modifications of such nature are exemplified in Fig. 3 and will be fully understood from the following.

The helper drive control system according to Fig. 3 is shown as applied to the three cylinder moulds CMI, 0M2 and 0M3 of the paper machine illustrated in Fig. 1. As apparent from Fig.3, and in accordance with Fig. l, a separate helper drive motor HMI, HMZ or I-IM3 is connected with each of the moulds by a transmission SHI, SHZ and SH3 respectively. According to Fig. 3, each of thesemotors has an armature HAI, HA2 or HA3 acted upon by a series field winding SFI,

SFZ or SF3 and a shunt-type field winding HFI,

HF2 and HF3, respectively. The armatures and series connected field winding of the three helper drive motors HMI, HM2 and Hit/l3 are connected to the circuit C4 of the generator armature GA so that the motors lie in parallel to one another. The circuit Ct includes a series-connected resistor R5 for measuring the current output of the generator. The generator GN has a single field winding GF connected in series with the armature RA of a regulating generator RG. The connecting circuit (35 includes a resistor R6 and contains a self-exciting field winding RFG of the regulating generator v RG in shunt connection. The regulator RG has two additional field windings REA and RFS. RF i represents the pilot field winding and is connected with the resistor R5 of circuit Cd, the connection being effected through a slide contact at R5 in order to adjust the voltage across RF K. Once the slide contact of R5 is adjusted, its position remains unchanged during the operation of the control system so that the pilot field produced by RF! is dependent upon the armature current of the main generator GN and hence on the feed current supplied to the three helper drive motors. The field winding RF5 of the regulator RG is connected to a constant direct current source which is represented by an exciter EX. This exciter has its armature EA connected in series with a self-energizing exciter winding EF3 and with a direct current output circuit C6. A shunt winding EFl of the exciter is connected with circuit Cl over an exciter rheostat EXR to permit adiustin the voltage of the exciter output current.

The armature GA of the main generator GN and the; armature BA 01' the regulator RG and EA of the exciter EX are mounted on a common shaft GSH which is driven by constant speed from a motor MT fed from a suitable current source such as the AC line denoted by A05. The motor MT operates at constant speed.

The above-mentioned shunt fields HFI, HF! and HF3 of the three helper drive motors are connected in parallel to the direct current circuit C6 fed from the exciter EX. Each connection leads over an individual adjusting rheostat MRI, MR2 and MR3 respectively, so that the basic torque or driving efi'ort of each helper drive motor can be adjusted in order to obtain the desired ratio relative to the torque of the other helper drive motors. The total torque or driving effort of all these helper drive motors is kept constant by the operation of the regulating generator RG. When varying the speed of operation of the master drive, as represented by the line shaft drive, the control system accordingv to Fig. 3 is adjusted automatically by the regulator.

The winding RF5 of the regulator RG, representing the pattern field of this generator, is connected with the circuit C6 over a potentiometric resistor R1 and a control relay CR. The control coil CRC of this relay is connected over a limit switch LSWI to the exciter circuit C6. The resistor R! has two slide contacts US and LS. The limit switch LSWI is associated with the master drive coupling, for instance the coupling MCL shown in Fig. l, the association being of the same typeas that of limit switch LSW with coupling MCL. That is, the limit switch LSWI, according to Fig. 3, is open when the master drive is at rest and is closed when the master drive is actuated by closing the master drive, coupling. The relay coil CRC acts on an armature CRA which carries two contacts RC3 and RC4. When the limit switch LSWI is open, the contact RC4 is closed. Inthis condition, the voltage effective at RF5 corresponds to the voltage drop between the upper terminal of R1 and the upper slide contact US. This voltage drop is adjusted at US in accordance with the standstill and starting conditions of the system. When the master drive is put in operation and, hence, the limit switch LSWI closed, the coil CRC is energized and the armature CRA attracted. In this condition, the contact RC4 is opened and the contact RC3 closed, so that now the upper slide contact US is disconnected and the lower slide contact LS rendered operative. The voltage across the pattern field winding RF5 corresponds now to the voltage drop from the upper terminal of R1 to the lower slide contact LS. This voltage drop is larger than the one previously effective, and cor responds to the normal operating conditions of the system. The latter voltage drop can be adjusted by means of the slide contact LS.

The regulatory operation of the system shown in Fig. 3 is essentially similar to that of the system previously described in connection with Fig. 2. The chosen adjustment of the slide contact LS determines the current condition in the feed circuitCd and, hence, the torque of each helper drive motor at which the excitation of the regu lating generator RG effected by the pilot field RF is neutralized by the pattern field RPS. As a result, the control system tends to maintain the torque of each helper drive motor at a selected magnitude.

It will be understood from the foregoing that helper drive systems the type described may also be applied for controlling the operation of the other helper drive motors HMl, I-I1VI5 and HMS shown in Fig. i. or the helper drive motors in other sections of the paper machine. Systems according to the invention are, of course, also applicable with machine units other than papermaking machines in which the operation of a drive is to be accurately controlled in dependence upon the operation of another drive, and especially in cases where the controlled drive effects an auxiliary or corrective function while the main driving energy is supplied by an independently operated master drive.

It will also be understood that various modifications of my invention other than those exemplified in the foregoing are available to those skilled in the art without departure from the essential features of the invention and within the scope of the claims attached hereto.

I claim as my invention:

1. With a master drive and a helper drive, the combination of a control system for said helper drive which comprises a D. C.-helper drive motor, a main D. C. generatorhaving a variable-voltage output circuit connected with said motor for" energizing said motor and a field circuit for controlling the voltage of said output circuit, means for driving said generator substantially in a given speed relation to said master drive, a separately driven regulating D. C. generator having a regulating output circuit connected with said main generator field circuit and at least three coacting field windings for elfecting a resultant volt age control on said regulating output circuit, one of said field windings being connected with said regulating output circuit to provide self-excitation for said regulating'generator, said output circuit of said main generator being conneoted with a second one of said windings to excite the latter in dependence upon an electric magnitude of the current supplied by said main generator to said helper drive motor, a D. C. current source connected with said third winding,

selectively adjustable circuit means associated with said source for providing said latter-winding with adjustable excitation, said circuit means being rated for causing said excitation to balance the eil'ect of said second winding on said regulat- .ing output circuit when said magnitude corre- 1 dc to the selected adjustment of said circuit With a master drive and a helper drive, the combination of a cor vol system for said helper drive 'wliiclii comp: a helper drive motor of variable vol ge-dcpei nt speed, a main genorator having a variahlevoltage output circuit connected with said motor and a field circuit for controlling the output voltage, means for driving generator substantitiilly in a given speed re lation to said master drive, a separately driven regulating generator having a regulating output circuit connected with said main generator field circuit and at least coacting field windings for effecting resultant voltage control on said regulating output circuit, one of said field windings being connected with said regulating output circui to provide self-excitation for said regulating g crater, said output circuit of said main generator being connected with a second one of said windings to excite the latter in dependence upon an electric magnitude of the current supplied by said main generator to said helper drive motor, a current source of substantially constant voltage connected with said third winding, selectively adjustable circuit means associated with said source for varying the voltage drop eflective across said latter winding in order to provide said latter winding with adjustable excitation, said circuit means being rated for causing said excitation to balance the eilect of said second winding on said regulating output circuit when said magnitude corresponds to the selected adjustment of said circuit means.

3. With a master drive and a helper drive, the combination of a control system for said helper drive which comprises a helper drive motor of variable voltage-dependent speed, a main generator having a variable-voltage output circuit connected with said motor and a field circuit for controlling the output voltage, means for driving said main generator substantially in a given speed relation to said master drive, a regulating generator having a regulating output circuit connected with said main generator field circuit, a

constant-speed motor in driving connection with said regulating generator, said regulating generator having at least three coacting field windlugs for effecting a resultant voltage control on said regulating output circuit, one of said field windings being connected with said regulating output circuit to provide self-excitation for said regulating generator, an impedance element arranged insaid output circuit of said main generator and connected with a second one of said windings to excite the latter in dependence upon an electric magnitude of the current supplied by said main generator to said helper drive motor, an exciter mechanically connected with said motor to be driven thereby simultaneously with said regulating generator for providing a constant exciter voltage, said exciter being connected with said third winding, and voltage-adjusting circuit means interposed between said exciter and said third winding for providing the latter winding with adjustable excitation, said circuit means being rated for causing said excitation to balance the eifectof said second winding on said regulating output circuit when said magnitude corresponds to the selected adjustment of said circuit means.

d. With a i'naster drive and a helper drive, the combination of a control system for said helper drive which comprises a helper drive motor of variable voltage-dependent speed, a main generator having a variable-voltage output circuit coniicctcd with said motor and a field circuit for oiling the output voltage, said main generoeingconnected with said main drive so as to driven thereby in a given speed relation to said main drive, a separately driven regulating generator having a regulating output circuit connected with said main generator field circuit and at three coacting field winding for effecting a resultant voltage control on said regulating output circuit, one of said field windings being connected with said regulating output circuit to provide self-excitation for said regulating generator, an impedance element arranged in said output circuit of said main generator and connected with a second one of said windings to excite the latter in dependence upon an electric magnitude of the current supplied by said main generator to said helper drive motor, a current source connected with said third winding, selectively adjustable circuit means associated with said source for providing said third winding with adjustable excitation, said circuit means being rated for causing said excitation to, balance the effect of said second winding on said regulating output circuit when said magnitude corresponds to the selected adjustment of said circuit means,

5. With a master drive and a helper drive, the combination of a control system for said helper drive which comprises a D, C.-helper drive motor for variable voltage operation, a main D. C. generator having an armature connected with said motor and a field circuit for controlling the voltage supplied to said motor, means for driving said generator armature substantially in a given speed relation to said master drive, a motor-generator set including a constant-speed motor and a D. C. regulating generator, said regulating generator having a self-exciting field winding, a pilot field winding, a pattern field winding, and a reg- .ulator armature acted upon by said three latter windings, said regulator armature being mechanically connected with said constant-speed motor and electrically connected with said generator field circuit and said self-exciting field winding to energize said circuit and said latter winding by a variable D. C. voltage, a resistance element connected between said main generator armature and said helper drive motor to measure the current flowing through said motor, said resistance element being connected with said-pilot field winding to excite the latter winding in dependence upon said current, a D. C. current source of constant voltage connected with said pattern winding, adjustable circuit means interposed between said source and said pilot field winding for adjusting the energization of said pilot field winding so as to balance the efiect caused on said armature of said regulating generator by said pilot field winding at a magnitude of said current corresponding to the selected adjustment.

6. In a machine unit having a master drive and a helper drive in driving connection with different machine parts of cooperative main and auxiliary functions respectively, said helper drive comprising, in combination, a drive motor having-an armature in driving connection with said corresponding machine part and two motor field windings acting on said armature, a main generator having a field circuit and an armature output circuit, said output, circuit being connected with said motor armature and one of said motor field windings, means for driving said main generator substantially in a given speed relation to said master drive, a regulating generator having a regulator armatureconnected with said main generator field circuit, a constant-speed motor in driving connection with said regulating generator, said regulating generator having a selfexciting field winding connected with said regulator armature, a pilot field winding and a pattern field winding coacting on said regulator armature so as to determine the output voltage impressed by said armature on said main generator field circuit, said pilot field winding and said pattern field winding being wound and rated for balancing their efiects under proper relative exciting conditions, means for driving said regulator armature at substantially constant speed, said armature output circuit of said main generator being connected with said pilot field winding so as to excite it in dependence upon the load current of said motor, a current. source of substantially constant voltage connected with said pattern field winding and with said other motor field winding, voltage adjusting means disposed between said sourceand said other motor field winding for selecting the datum speed of said helper drive motor, and further voltage adjusting means disposed between said source and said pattern field winding for selecting the magnitude of said current at which said effects of said pilot and pattern field windings are balanced.

7. In a machine unit having a master drive and a helper drive in driving connection with different machine parts of cooperative main and auxiliary functions respectively, said helper drive comprising, in combination, a D. C.-drive motor having an armature in driving connection with said corresponding machine part and two motor field windings acting on said armature, a main D. C. generator having a field circuit and an armature output circuit, said output circuit being connected with said motor armature and one of said motor field windings, means for drivingsald main generator substantially in a given speed relation to said master drive, a motor-generator set including a constant-speed motor and a D. C. regulating generator, said regulating generator having a self-exciting field winding, 2. pilot field winding, a pattern field winding, and a regulator armature acted upon by said three latter windings, said pilot field winding and said pattern field winding being wound to act differentially on said regulator armature, said regulator armature being mechanically connected with said constant-speed motor and electrically connected with said generator field circuit and said self-exciting field winding to energize said circuit and said latter winding by a variable D. C. voltage,

a resistance element connected between said main generator armature and said helper drive motor to measure the current flowing through said motor, said resistance element being connected with said pilot field winding to excite the latter winding in dependence upon said current, a D, C. exciter mechanically connected with said constant-speed motor to supply a substantially constant pattern voltage, said exciter being electrically connected with said pattern field winding and with said other motor field winding, voltage adjusting means disposed between said exciter and said other motor field winding for selecting the datum speed of said helper drive motor, and further voltage adjusting means disposed between said exciter and said pattern field winding for selecting the magnitude of said cur rent at which said effects of said pilot and pattern field windings are balanced.

8. In a machine unit having a master drive and a helper drive in driving connection with different machine parts of cooperative main and auxiliary functions respectively, said helper drive comprising, in combination, a drive motor having an armature in driving connection with said corresponding machine part and two motor field windings acting on said armature, a main generator having a generator armature and a generator field winding, said generator armature being mechanically connected with said master drive to be actuated in a given speed relation thereto and electrically connected with said motor armature and one of said motor field windings to supply them with controlled voltage, a motorgenerator set including a constant-speed motor and a regulating generator, said regulating generator having a self-exciting fieldwinding, a pilot field winding, a' pattern field winding, and a regulator armature acted upon by said three latter windings, said pilot field winding and said pattern field winding being wound and rated for balancing their effects on said regulator armature under proper relative exciting conditions, said regulator armature being mechanically connected with said constant-speed motor and electrically connected with said main generator field winding and said self-exciting field winding to energize said latter two windings, circuit means disposed between said main generator armature and said motor armature for measuring the current traversing said motor armature, said circuit means being connected with said pilot field winding to excite it in dependence upon said current, an exciter mechanically connected with said constant-speed motor to generate a substantially constant pattern voltage, said exciter being electrically connected with said pattern field winding and with said other motor field winding, voltage adjusting means disposed between said exciter and said other motor field winding for selecting the datum speed of said helper drive motor, and further voltage adjusting means disposed between said exciter and said pattern field wind ing for selecting the magnitude of said current at which said effects of said pilot and pattern field windings are balanced.

9. In a machine unit having a master drive and a helper drive in driving connection with different machine parts of cooperative main and auxiliary functions respectively, said master drive having substantially constant speed and said helper drive being combined with a variablespeed control system which comprises, in combination, a helper drive motor, a main generator having a variable-voltage output circuit connected with said motor and a field circuit for controlling the output voltage, a constant-speed motor in driving connection with said main generator, a constant-speed regulating generator having at least three coaoting field windings for eifecting a resultant voltage control on said regu' lating output circuit, one of said field windings being connected with said regulating output circult to provide self-excitation for said regulating generator, said other two windings of said regulator generator being wound for differential action, an impedance element arranged in said output circuit of said main generator and connected with one of said differential windings to excite it in dependence upon an electric magnitude of the current supplied by said main generator to said helper drive motor, a constant-speed exciter for generating a substantially constant voltage, said exciter being connected with said other diiferential winding, selectively adjustable circuit means associated with said source for providing said latter winding with adjustable excitation, said circuit means being rated for causing said differential windings to balance their effects on said regulating output circuit when said magnitude corresponds to the selected adjustment of said circuit means.

10. In a machine unit having a master drive and a helper drive in driving connection with different machine parts of cooperative main and auxiliary functions respectively, said helper drive comprising, in combination, a helper drive motor, a main generator having a variable-voltage output circuit connected with said motor and a field circuit for controlling the output voltage, a regulating generator having at least three coacting field windings for effecting a resultant voltage control on said regulating output circuit, one of said field windings being connected with said regulating output circuit to provide self-excite tion for said regulating generator, said other twl windings of said regulator generator being WOUlli for differential action, an impedance element ar ranged in said-output circuit of said main gen erator and connected with one of said differential windings to excite it in dependence upon ar electric magnitude of the current supplied b: said main generator to said helper drive motor an exciter for generating a substantially con stant voltage, said excifer being connected witl said other differential winding, selectively adjustable circuit means associated with said S0lll'C1 for providing said latter winding with adjustabli excitation, said circuit means being rated to: causing said differential windings to balance theii effects on said regulating output circuit when saic magnitude corresponds to the selected adjustmentof said circuit means, and-a constant-speed motor mechanically connected with said main generator, regulating generator and exciter for driving them simultaneously at substantially constant speed.

11. In a machine unit having a master drive and a helper drive in driving connection with different machine parts of cooperative main and auxiliary functions respectively, the combination of a helper drive motor having an armature in driving connection with said machine part of auxiliary function and two motor field windings acting on said armature, a main generator having a field circuit and an armature output circuit, said output circuit being connected with said motor armature and one of said motor field windings, means for driving said main generator substantially in a given speed relation to said master drive, a motor-generator set including a constant-Speed motor and a D. C. regulating generator, said regulating generator having a self-exciting field winding, a pilot field winding, a pattern field winding, and a regulator armature acted upon by said three latter windings, said regulator armature bein mechanically connected with. said constant-speed motor and electrically connected with said generator field circuit and said self-exciting field winding to energize said circuit 'and said latter winding by a variable D. C. voltage, a resistance element connected between said main generator armature and said helper drive motor to measure the current flowing through said motor, said resistance element being cormected with said pilot field winding to excite the latter winding in dependence upon said current, a constant voltage source connected with said pattern field winding and with said other motor field winding, voltage adjusting means disposed between said source and said other motor field winding for selecting a, constant component motor excitation, further voltage adjusting means disposed between said source and said pattern field winding for selecting the magnitude of said current at which said effects of said pilot and pattern field windings are balanced, circuit control means also disposed between said source and said pattern field winding for adjusting the voltage across said pattern field winding to starting conditions, said circuit control means including a relay, master control means for controlling the driving effect of said master drive on said machine part of main function, and switch means responsive to said master control means and connected with said relay for causing said relay to control said circuit control means so as to adjust said pat-tern field voltage to starting and normal operating conditions in accordance with the inoperative and operative condition respectively or said master control means.

, 12. In a machine unit having rotary cylindric parts arranged in operative relation to an peripheral contact with asheet-like body of maparts in combination with a system for controlling the operation of said dependent drive in relation to that of said independent drive, said combination comprising a D. Q-drive motor connected with said other cylindric part to drive the latter part, a main D. 0. generator having a variablevoltage output circuit connected with said motor for energizing said motor and a field circuit for controlling the voltage of said output circuit, means for driving said main generator in a given speed relation to said independent drive, a separately driven D. C. regulating generator having a regulating output circuit connected with said main generator field circuit and at least three coacting field windings for efiecting a resultant voltage control on said regulatin output circuit, one of said field windings being connected with said regulating output circuit to provide self-excitation for said regulating generator, sai other two windings of said regulator generator being wound for diiierential action, an impedance element arranged in said output circuit of said main enerator and connected with one of said differential windings to excite it in dependence upon an electric magnitude of the current supplied by said main generator to said motor, a D. C. current source connected with said other difierential winding, selectively adjustable circuit means associated with said source for providing said latter winding with adjustable excitation, said circult means being rated for causing said excitation to balance the eifect of said diiferential winding on said regulating output circuit when said magnitude corresponds to the selected adjustment of said circuit means.

13. With a paper machine having a roll press, a suction drum, a transport band passing over said drum and through said press for supplying pulp to said press, and a master drive for actuating said press, the combination of a helper drive motor coupled with said drum for driving it so 80 as to relieve said band of tensional stress, a main generator having a variable-voltage-output circuit connected with said motor and a field circuit for controlling the output voltage, means for driving said main generator substantially in a 55 output circuit to provide self-excitation for said 55 regulating generator, said other two windings of said regulator generator being wound for differential action, an impedance element arranged'in said output circuit of said main generator and connected with one of said differential windings 70 to excite it in dependence upon an electric magnitude of the current supplied by said main generator to said helper drive motor, an exciter mechanically connected with said motor to be ing generator for providing a constant exciter voltage, said exciter being connected with said other diiierential winding, and voltage-adjusting circuit'means interposed between said exciter and said latter'winding for providing'said latter winding with adjustable excitation, said circuit means being rated for causing said excitation to balance the effects of'said difierential windings on said regulating output circuit when said magnitude corresponds to the selected adjustment oi said circuit means.

14. With a paper machine having. a roll press. a suction drum, a transport band passing over said drum and through said press for supplying pulp to said press, a line shaft drive, and coupling means for establishing a driving connection of said line shaft drive with said press, the combination of a helper drive motor having an armature in driving connection with said drum and two motor field windings acting on said armature, a main generator having a field circuit and an armature output circuit, said output circuit being connected with said motor armature and one of said motor field windings, said main generator being mechanically connected to said line shalt drive to be driven in a given speed relation to said press, a motor-generator set including a constant-speed motor and a D. C. regulating generator, said regulating generator having a selfexciting field winding, a pilot-field winding, a pattern field winding, and aregulator armature acted upon by said three latter windings, said pilot field'winding and said pattern field winding being wound for differential action, said regulator armature being mechanically connected with said constant-speed motor and electrically connected with said generator field circuit and said self-exciting field winding to energize said circuit and said latter winding by a variable D. C. voltage, a resistance element connected between said main generator armature and said helper drive motor to measure the current flowing through said motor, said resistance element bein connected with said pilot field winding to excite I the latter winding in dependence upon said current, a constant voltage source connected with said pattern field winding and with said other motor field winding, voltage adjusting means disposed between said source and said other motor field winding for selecting a constant component motor excitation, further voltage adjusting means disposed between said source and said pattern field winding for selecting the magnitude of said current at which said eflects of said pilot and pattern field windings are balanced, circuit control means. also disposed between said source and said pattern field winding for adjusting the voltage across said pattern field winding to starting conditions, said circuit control means including a re-- lay, and switch means associated with said coupling means so as to be controlled by the actuation of said coupling means, said switch means being connected with said relay for causing it to control said circuit control means so as to adjust said pattern field voltage to starting and normaloperating conditions in accordance with the inoperative and operative condition respectively of said drum.

15. In a machine unit having rotary cylindric parts arranged in operative relation to and peripheral contact with a sheet-like body of material passing through the unit when said parts are in operation, an independent drive for rotating one of said cylindric parts, and a dependent drive driven thereby simultaneously with said regula-t- (l ng another one of said cylindric parts in combination with a system for controlling the operation of said dependent drive in relation to that of said independent drive, said combination comprising an electric motor in mechanical driving connection with said other cylindrie part, an electric feeding device having a varlable-voltage reed circuit connected with said motor and two differential control means for determining the voltage of said feed circuit so as to control thereby the operation or said motor, one of said i'eed control means being connected with said independent drive for providing in said feed circuit a voltage representative of the speed of said independent drive, an electric regulating device having a regulating output circuit connected with said other control means of said feeding device for modifying said voltage in said feed circuit, said regulating device having two control members for effecting a resultant voltage control on said regulating output circuit, an impedance element connected with said feed circuit and with one of said members to control the latter member in dependence upon an electric magnitude of the current in said feed circuit, a separate current source connected with said other control member and provided with selectively adjustable circuit means for varying the control efiect of said other member, said circuit means being rated relatively to said source and other member for causing said control effect to neutralize that of said first control member on said regulating output circuit when said magnitude has a given value depending upon the selected adjustment of said circuit means.

16. In a machine unit having a master drive and a helper drive in driving connection with different machine parts of cooperative main and auxiliary functions respectively, said helper drive comprising, in combination, a voltage-responsive variable speed motor in driving connection with said machine part of auxiliary function, a controllable electric feeding device having three control means for cooperatively determining the voltage of said feed circuit so as to control thereby the operation of said motor, one of said feed control means being connected with said master drive for providing in said feed circuit a voltage representative of the speed of said master-driven machine part, an energizing circuit connected with a second one of said feed control means and including an adjustable circuit member for providing a constant energization of selective magnitude in order to superpose on the output voltage of said feeding device a constant modification, a controllable electric regulating device having a regulating output circuit connected with said other control means of said feeding device for further modifying said output voltage in said feed circuit, said regulating device having two diflerential control members for effecting a resultant voltage control on said regulating output circuit, an impedance element connected with said feed circuit and with one of said members to control the latter member in dependence upon an electric magnitude of the current in said feed circuit, a separate current source connected with said other control member and provided with selectively adjustable circuit means for varying the control efiect of said other member, said circuit means being rated relatively to said source and other member for causing said control effect to neutralize that of said first control member on said regulating output circuit when said magnitude has a given value depending upon the selected adjustment of said circuit means.

1'7, In a machine unit having rotary cylindric parts arranged in operative relation to and peripheral contact with a sheet-like body of material passing through the unit when said parts are in operation, an independent drive for rotating one of said cylindric parts, and a dependent drive ior rotating another one of said cylindrlc parts in combination with a system for controlling the operation of said'dependent drive in relation to that of said independent drive, said combination comprising an electric motor in mechanical driving connection with said other cylindric part, an electric feeding device having a variable-voltage feed circuit connected with said motor and two separate control means for determining the voltage of said feed circuit so as to control thereby the operation of said motor, one of said feed control means being connected with said independent drive for providing in said feed circuit a voltage representativeof the speed of said independent drive, an electric regulating device having a regulating output circuit connected with said other control means of said feeding device for modifying said voltage in said feed circuit, said regulating device having two diiierential control members for effecting a resultant voltage control on said regulating output circuit, an impedance element connected with said feed circuit and with one of said members to control the latter member in dependence upon an electric magnitude of the current in said feed circuit, a separate current source of constant voltage connected with said other control member to excite the latter member, adjustable circuit means connected with one of said control members for selectively varying the control effects of said control members relative to each other so as to cause said effects to balance each other when said magnitude has a given value depending upon the adjustment of said circuit means.

18. In a machine unit having a master drive and a helper drive in driving connection with different machine parts of cooperative means and auxiliary functions respectively, the combination of a helper drive motor having an armature in driving connection with said machine part of auxiliary function and two motor field windings acting on said armature, a main generator having a field circuit and an armature output circuit, said output circuit being connected with said motor arma ture and one of said motor field windings, means for driving said main generator substantially in a given speed relation to said master drive, a motor-generator set including a constant-speed motor and a D. C. regulating generator, said regulating generator having a self-exciting field winding, a pilot field winding, a pattern field winding acting in opposition to said pilot field winding, and a regulator armature acted upon by said three latter windings, said regulator armature being mechanically connected with said constant-speed motor and electrically connected with said generator field circuit and said self-exciting field winding to energize said circuit and said latter Winding by a variable D. C. voltage, a resistance element connected between said main generator armature and said helper drive motor to measure the current flowing through said motor, said resistance element being connected with said pilot field winding to excite the latter Winding in dependence upon said current, a constant voltage source connected with said pattern field winding and with said other motor field winding, adjustable resistance means connected with one of said pattern and pilot field windings for adjusting the of a helper drive motor having an armature in driving connection with said machine part of auxiliary function and two motor field windings acting on said armature, a main generator having a field circuit and an armature output circuit, said output circuit being connected with said motor armature and one of said motor field windings, means for driving said main generator substantially in a given speed relation to said master drive, a motor-generator set including a constant-speed motor and a D. C. regulating generator, said regulating generator having a selfexciting field winding, a pilot field winding, a pattern field winding acting in opposition to said pilot field winding, and a regulator armature acted upon by said three latter windings, said regulator armature being mechanically connected with said constant-speed motor and electrically connected with said generator field circuit and said self-exciting field winding to energize said circuit and said latter winding by a variable D. C. voltage, a resistance element connected between said main generator armature and said helper drive motor to measure the current flowing through said motor, said resistance element be-. ing connected with said pilot field winding to excite the latter winding in dependence upon said current, a constant voltage source connected with said pattern field winding and with said other motor field winding, adjustable resistance means connected with one of said pattern and pilot field windings for adjusting the control effects of said latter windings relative to each other so as to cause said effects to balance each other when said magnitude has a given value depending upon the adjustment of said circuit means, a control cit-- cult also connected with one of said pattern and pilot field windings, said control circuit containing relay means and an impedance member controlled by said relay means for affecting the voltage across the connected winding-master control means for controlling the driving effect of said master drive on said machine part of main function, and switch means responsive to said master control means and connected with said relay means for causing said control circuit to adjust said relative control eiiects to starting and normal operating conditions in accordance with the inoperative and operative condition respectively of said master drive.

20. A drive system for a machine unit having a master drive and a helper drive and comprising, in combination, a D. C.-helper drive motor,

a main D. C. generator having a variable-voltage armature circuit connected with said motor for energizing said motor and a field circuit for controlling the voltage of said armature circuit, means for driving said main generator substantially in a given speed relation to said master drive, a separately driven regulating D. C. generator having a regulating output circuit connected with said main generator field circuit and at least two field windings acting difierentially with respect to each other for effecting a resultant voltage control on said regulating output circuit, one of said field windings being connected with said armature circuit of said main generator so as to be excited in dependence upon an electric magnitude of the current supplied by said main generator to said helper drive motor, direct-current circuit means connected with said other winding and having adjustable circuit means for providing said latter winding with adjustable excitation.

21. A drive system for a machine unit having a master driye and a helper drive and comprising, in combination, a D. C. helper drive motor, a main D. C. generator connected with said motor for supplying energization thereto, means for driving said main generator substantially in a. given speed relation to said master drive, means disposed for regulating said energization and including a regulating D. C. generator having an armature output circuit connected with said generator for varying the voltage across said motor, said regulating generator having two oppositely acting field windings, one being connected with said motor so as to be excited in accordance with the current flowing through said motor, and direct-current circuit means connected with said other field winding and having adjustable circuit means for providing said latter winding with adjustable excitation, said circuit means bein rated for causing said excitation to balance the effect of said first field winding on said armature output circuit when the magnitude of said current corresponds to the-selected adjustment of said circuit means.

WALTER R. HARRIS. 

